The present invention relates to a plate lockup apparatus mounted in a plate cylinder of a printing press so that leading and trailing edges of a plate to be wound around the plate cylinder are fixed within a gap axially formed in the outer circumferential surface of the plate cylinder.
A gap having a substantially rectangular sectional shape is formed along the entire length in the outer circumference of each plate cylinder in each printing press. A plate lockup apparatus consisting of a leading-side lockup device for gripping the leading edge of the plate and a trailing-side lockup device for gripping the trailing edge of the plate is fixed on the bottom surface of the gap to extend in the axial direction of the plate cylinder.
Each of the conventional leading- and trailing-side lockup devices has an elongated lockup table extending in the axial direction of the plate cylinder, a plurality of gripper plates, swingably supported at an edge portion of this lockup table by a plurality of bolts, for gripping or releasing the plate with or from the lockup table, and a plurality of cams which can be respectively engaged with gaps at the leading edges of the gripper plates. The plurality of axially parallel cams are pivotally fixed along the axis. A plurality of compression coil springs are interposed between the lockup table and the gripper plates to bias the gripper plates in an open direction. The lockup table in the trailing-side lockup device is supported on the bottom of the gap to be movable along the circumferential direction of the plate cylinder. A plurality of plate tension bolts are threadably engaged with a plurality of longitudinal portions of the lockup table so that the distal ends of the bolts abut against the wall surface which defines the gap.
With the above arrangement, in order to mount a plate on a plate cylinder, when a cam shaft of the leading-side lockup device is pivoted, the gripper plates which are divided in the axial direction of the plate are released upon disengagement from the cams and are simultaneously opened by the elastic forces of the compression coil springs. An end of the plate is inserted between the leading-side lockup device and the corresponding lockup table. When the cam plate is pivoted in the direction opposite to the direction described above, the gripper plates are pivoted against the elastic forces of the compression coil springs by the behavior of the cams and are closed, thereby gripping the leading edge of the plate. After the leading edge of the plate is gripped, the plate is wound around the plate cylinder. The trailing edge of the plate is gripped by the trailing-side lockup device in the same manner as the leading edge. The plate tension bolts are tightened to move the trailing-side lockup device in the circumferential direction of the plate cylinder, so that the plate is brought into tight contact with the plate cylinder. Since spring members are interposed between the trailing-side lockup device and the gap, when the plate tension bolts are loosened, the plate lockup device is moved toward the wall surface of the gap by the spring forces of the spring members, thereby tightening the plate.
In the conventional plate lockup apparatus having the above arrangement, however, since the plate is inserted between the lockup table and the gripper plates from a tangential direction of the plate cylinder while the plate end portion is not bent but kept straight, it is technically very difficult to grip the plate straight without any deformation. The tensions along the widthwise direction become nonuniform upon tightening of the plate. An error tends to occur in the reference printing point.
In order to solve this problem, an apparatus disclosed in Japanese Patent Laid-Open No. 1-127346 is proposed. In this apparatus, the lockup tables and the gripper plates are disposed in the radial direction of a plate cylinder so that a trailing-side gripper surface of the plate conventionally formed in the circumferential direction of the plate cylinder is formed in the radial direction of the plate cylinder. The edge of the plate is bent at a right angle by an external bending machine.
With this arrangement, after the leading edge of the plate is gripped, the bent portion of the trailing edge portion of the plate wound around the circumferential surface of the plate is inserted between the lockup tables and the gripper plates. The gripper plates are swung by a cam mechanism to grip the bent portion of the plate. The trailing-side lockup device as a whole is circumferentially moved to unfirmly mount the plate, thereby bringing the plate into tight contact with the surface of the plate cylinder.
In such a sheet-fed press, when an old plate is replaced with a new plate due to changes in contents of printed matters, the plate cylinder is pivoted to cause the trailing-side cam shaft to oppose an operating position, and the trailing-side cam shaft is pivoted to open the trailing-side lockup device. One end of the plate which is released from gripping is kept held, and the plate cylinder is rotated so that the leading-side lockup device opposes the operating surface. The leading-side ca:n shaft is pivoted to open the leading-side lockup device to release the other end of the plate from gripping, thereby removing the old plate. Thereafter, opening/closing of the plate lockup devices and the pivotal operation of the plate cylinder are repeated to mount the new plate.
In the conventional plate lockup apparatus having the above arrangement, plate gripping and plate tightening are performed by separate mechanisms, and the structure is undesirably complicated. In addition, the number of operating steps is increased, and good operability is not always obtained, thus presenting the first problem.
As described above, since the plate gripper surface is opened/closed, the cam shaft must be manually pivoted. The number of operating steps is increased, operability is degraded, and much labor is required. In addition, a preparation time is undesirably prolonged to degrade productivity, thus presenting the second problem.
Since the pivotal operation of the leading-side cam shaft for opening the leading-side lockup device and the pivotal operation of the trailing-side cam shaft for opening the trailing-side lockup device must be performed at different phases of the plate cylinder, a plate replacement time is undesirably prolonged, the total preparation time is prolonged, and the productivity is degraded, thus presenting the third problem.